US20050038436A1 - System and method for stabilizing a portion of the spine - Google Patents

Abstract

Anatomically contoured anterior cervical plates with bone ingrowth surfaces, providing for intersegmental compressive preloading, and a rigid and locked interface to all of the bone screws, with those engaging the vertebrae deployed in highly convergent pairs. The bone screws have a tapered self-tapping leading end, an increasing root diameter with a generally constant outer diameter with a thread that is narrow and sharp throughout and an enlarged head portion capable of an interference fit to the receiving holes of the plate. Instrumentation consists of plate holders, a compression apparatus and a pilot hole forming device that interlocks with the plate. Methods for spinal compression and bone hole preparation are provided.

Description

RELATED APPLICATIONS
• This application is a continuation of application Ser. No. 10/253,678, filed Sep. 24, 2002, which is a divisional of Ser. No. 09/754,733, filed Jan. 4, 2001, now U.S. Pat. No. 6,454,771, which is a continuation of application Ser. No. 09/022,293, filed Feb. 11, 1998, now U.S. Pat. No. 6,193,721, which claims the benefit of U.S. provisional application Ser. No. 60/037,139, filed Feb. 11, 1997; all of which are incorporated herein by reference. Application Ser. No. 09/022,344, filed Feb. 11, 1998, now U.S. Pat. No. 6,139,550, is incorporated herein by reference.
BACKGROUND OF THE INVENTION
• 1. Field of the Invention
• The present invention relates generally to implants, method, and instrumentation for fusion of the human cervical spine from the anterior aspect, and in particular to plate systems for aligning and maintaining adjacent cervical vertebrae in a selected spatial relationship during spinal fusion of those vertebrae.
• 2. Description of the Related Art
• It is current practice in the art to use cervical plating systems for this purpose. Such systems are composed essentially of plates and screws for aligning and holding vertebrae in a desired position relative to one another. The earliest such devices consisted of stainless steel plates and screws and required that the screws passed entirely through the vertebrae and into the spinal canal in order to engage the strong bone tissue (the posterior cortex) of the vertebral bodies. This required the ability to observe or visualize this area radiographically, which is not always possible, especially in the lower cervical spine where the vertebrae may be hidden radiographically by the shoulders.
• In order to form holes in the vertebral bodies for insertion of each screw, a drilling operation was performed, followed by a tapping operation. Each of these operations involved the passage of an instrument entirely through the associated vertebral body and into the spinal column. Thus, these instruments come into close proximity to the spinal cord and the dural sac which are in close proximity to the back surfaces of the vertebral bodies. Any procedure which introduces an object into the spinal canal presents serious risks which are of concern to the surgeon.
• The conventional technique of forming a bone screw receiving hole in vertebral bodies by drilling has a number of significant disadvantages. For example, drilling removes bone material, leaving a void and resulting in a loss of bone material. Drilling also causes microfracturing of the bone at the drill bit-bone interface and the resulting fracture lines tend to propagate in directions perpendicular to the wall of the hole. More specifically, the bone material is essentially a type of ceramic which exhibits a brittle pattern of fracture formation and propagation in response to drilling. Furthermore, drilling generates heat which can result in thermal necrosis of the bone material precisely at the interface between the bone and a subsequently installed screw, where necrosis is most harmful. Any bone which does experience necrosis will subsequently be resorbed by the body as part of the bone repair process and this can lead to the loosening of the screw.
• Another problem with drilling is that the path of the drill bit is difficult to control and since the drill bit operates by rotation, it can wind up soft tissue about the associated plate. In addition, unless great care is taken, the drill bit may be driven significantly past the posterior cortex and cause irreparable harm within the spinal canal. Finally, a drill bit may bind and fracture within the vertebral body and can then cause serious injury as the still rotating portion of the drill bit passes into the wound, while the portion of the bit which has broken off may either protrude dangerously from the vertebral body or may be broken off flush with the upper surface of the body so as to be irretrievably embedded therein. In any event, the steps that must be taken to retrieve the broken-off portion of a drill bit will inevitably prolong and complicate the surgical procedure.
• In known plating systems, there have been problems with loosening and failure of the hardware, breakage of the screws and plates, and backing out of screws into the patient's throat area. These occurrences generally require further surgical procedures to replace the broken parts or the plates and screws entirely, and to repair any damage that may have been caused.
• Other problems which have been encountered with known systems result from the failure of the screws to achieve a sufficient purchase in the bone and the stripping of the screws.
• Also, the use of the known plating systems may result in a loss of lordosis, which is the normal curve of the cervical spine when viewed from the side.
• Known plating systems additionally experience problems in connection with those procedures where bone grafts are placed between vertebral bodies to achieve an interbody fusion which heals by a process called “creeping substitution”. In this process, bone at the interface between the graft and a vertebra is removed by a biological process which involves the production of powerful acids and enzymes, as a prelude to invasion of the interface by living tissue and the deposition, or growth, of new bone. While the plates allow for proper alignment of the vertebrae and their rigid fixation, they can therefore, at the same time unfortunately, hold the vertebrae apart while the resorption phase of the creeping substitution process forms gaps in the bone at the fusion site with the result that the desired fusion does not occur. Such failure is known as pseudoarthrosis. When such a failure occurs, the hardware itself will usually break or become loosened from the spine, thus requiring a further surgical procedure to remove the broken components and another surgical procedure to again attempt fusion.
• In response to the problems described above, a second generation of plating systems has been developed and/or proposed. These include a system disclosed in U.S. Pat. Nos. 5,364,399 to Lowery and 5,423,826 to Morscher, as well as cervical spine locking plating systems offered by SYNTHES Spine, the DANEK ORION plate, the CODMAN SHURTLEFF plate, and the SMITH NEPHEW RICHARDS plate, among others. The systems' forming members of this second generation have a number of common properties. They are all made of either a titanium alloy or pure titanium rather than stainless steel, to minimize adverse tissue reactions and are MRI compatible, which stainless steel is not. The screws and the plates have been given increased thickness in order to achieve increased strength. The screws have larger diameters to improve their purchase without requiring that they engage the posterior cortex of the vertebral bodies. Some mild longitudinal contouring of the plates is employed to allow for some lordosis, and/or limited transverse contouring to better follow the generally curved aspect of the front of the vertebral bodies. Mechanisms are employed for securing the vertebral bone screws to their associated plates in a manner to prevent the screws from backing out. While this second generation of plating systems represents a significant improvement over earlier systems, certain existing problems persist, while new problems have been created.
• For example, since the screws no longer extend into the posterior cortex, it is common for the threads in the tapped screw hole to become stripped and for the screws to fail to gain a suitable purchase. In addition, screw breakage continues to be experienced and occurs most commonly at the junction of the screw to the posterior aspect of the plate. The screws employed in both the SYNTHES system and the SMITH NEPHEW RICHARDS system are particularly vulnerable to this problem because those screws are hollow at the level where they attach to the plate to permit the internal reception of locking screws.
• In an attempt to prevent screw to plate junction breakage of the screw, more recent designs of screws have an increasing root diameter from tip to head, which thus far has resulted in a near useless stubby and blunt thread near the screw head with little holding power and little tactile feedback to the surgeon to signal the completion of tightening prior to stripping of the screw within the bone. Based on empiric studies testing these prior art screws, the use of a pretapped hole, rather than a self-tapping screw, was found to be preferred for pullout strength and thus these screws have not been self-tapping and thus the screw holes must be pre-tapped. Since the thread cutting portion of a tap is necessarily sharp and rotated to work, there is a serious risk of damage to the surrounding soft tissues when it is used. This is compounded by the fact that the plates employed in these systems do not provide sufficient long axis contouring to make full allowance for lordosis and do not have sufficient transverse contouring to prevent rocking of the plate about its longitudinal axis and to conform to the anterior shape of the vertebral bodies, so that these plates do not prevent soft tissue from creeping in from the sides and beneath the screw holes thus exposing these tissues to damage by the drill and the tap. While it is possible, at the time of surgery, to make some change in the contouring of these plates, this is generally limited to contouring of the longitudinal axis and quite often causes distortion of the plate's bone screw holes and screw hole to plate junctions in a manner which has an adverse effect on the screw-plate interlock. Lack of proper contouring prevents these plates from having an optimally low profile relative to the spine.
• In some of the second generation cervical plating systems, screw backout continues to occur, because these plates could not be designed to allow for the locking of all of the screws. Specifically, while the designers of these plates recognized the importance of securing the bone screws to the plates, they were unable to lock all of the screws and had to settle for leaving some of the screws unlocked.
• Furthermore, several of these second generation systems utilize tiny and delicate “watchmaker” parts to achieve interlocking. These parts are characterized by the need to engage them with particularly delicate small ended screw drivers. These interlocking components are easily rendered ineffective by any effort to alter the contours of a plate during surgery.
• Despite the improvement of these second generation plating systems over the first problems, the problems still persist, the most important of which is pseudoarthroses, and particularly “distraction pseudoarthroses”. Although these second generation plates have clearly led to an increase in fusion rate, when a failure to produce fusion occurs, it is generally accompanied by bone resorption along a line at the graft-to-vertebra junction, which can be seen on a radiograph.
• In the case of the weak first generation plates and screws, the plates might hold the vertebrae apart, preventing fusion, but only until the hardware would break, relieving the distraction, and then allowing the fusion to occur. The second generation systems of plates are too strong to allow this to occur, thus requiring further surgical procedures for the correction of the pseudoarthroses.
• Compression plates are well known and are widely used in orthopedic surgery for the stabilization of tubular bones, and sometimes also flat bones. Such plates may rely on some external compression means or may be self-compressing, relying on the ability of the screw head to slide within a ramped slot such that the tightening of the bone screws through the plate imparts a linear motion perpendicular to the screw axes. U.S. Pat. No. 5,180,381 discloses an attempt to employ such a mechanism in connection with anterior spinal fixation.
• However, it has been found that all of the proposed self-compressing plating systems have in common the need for a screw to engage both a proximal and a distal cortex, (bone casing of very dense bone material), so as to anchor the screw tip in a manner to allow the plate to move relative to the screw when tightened rather than allowing the plate to drag the screw off axis. However, as already discussed earlier herein, when a screw is to engage the posterior cortex of the vertebral body, it is necessary for the drill and the tap which form the screw hole, as well as the screw tip itself, to all enter the spinal canal, thereby exposing the spinal cord to damage.
• While the system disclosed in U.S. Pat. No. 5,180,381 avoids such danger by engaging the vertebral body end plate instead of the posterior vertebral body cortex, the path of the screw is of necessity quite short, so that there is very little opportunity for the screw threads to achieve additional purchase within the vertebral body. It would therefore appear that to the extent that the device disclosed in U.S. Pat. No. 5,180,380 is able to achieve its stated objectives, it would pull the front of the spine together more than the back and would not appear to compress the back of the vertebral bodies at all, thus producing an undesirable iatrogenic loss of the normal cervical lordosis. Such a situation is disruptive to the normal biomechanics of the cervical spine and potentially quite harmful.
• The creation of compression between adjacent vertebrae would offer a number of advantages, including reduced distraction pseudoarthrosis, increased surface area of contact between the graft and vertebrae as slightly incongruent surfaces are forced together, increased osteogenic stimulation, since compressive loads stimulate bone formation, and increased fusion graft and spinal segment stability.
• Among the new problems created by these second generation systems is a tendency for the small “watchmaker” parts used to lock the bone screws to the plate to fall off of the driver used for attaching those parts, or out of the associated plates and to become lost in the wound. In addition, these small parts are quite fragile and require specialized additional instruments for their insertion and/or manipulation. Furthermore, incorrect bone screw placement relative to the axis of a plate hole may render the screw locking mechanism unworkable or may cause sharp and jagged shavings of titanium to be formed as a locking screw is driven into contact with an improperly seated bone screw. The means for establishing bone screw to plate hole alignment and preparation are less than reliable. Furthermore, most of these second generation systems lack a reliable and effective means for positioning and holding the plate during attachment.
• Specific features of various prior art systems will be summarized below.
• The system disclosed in U.S. Pat. Nos. 5,364,399 and 5,423,826, cited earlier herein, includes a thin stainless steel plate which allows for side-by-side or offset bicortical screw placement, the plate having a combination of screw holes and slots.
• The “Acromed” system includes a titanium plate and screws which require bicortical screw placement. This system does not include any locking means for the bone screws.
• The system disclosed in U.S. Pat. No. 5,180,381 includes an “H” shaped plate having a combination of ramped slots and a hole which requires bicortical screw placement at a 45° angle to the plane of the plate. This patent discloses that this angular positioning is for the purpose of producing compression.
• The SYNTHES Morscher plate system employs hollow, slotted screw heads. The screws are placed unicortically so that the heads, when properly aligned, come to rest in the upper portion of the plate holes. The upper portion of each screw is internally threaded to receive a tiny screw which is screwed into the bone screw head in order to increase the interference fit between the bone screw head and the wall of the associated plate hole.
• In the system disclosed in U.S. Pat. Nos. 5,364,399 and 5,423,826, use is made of pairs of unicortical bone screws that may be locked in place at both ends of the associated plate by locking screws which have a small diameter shank and a large head. At each end of a plate two bone screws may be locked in place by a single locking screw which is situated between the bone screws. Generally, the plate is provided, between its two ends, with a diagonal slot or slots for receiving one or more additional screws, each additional screw being securable in a bone graft or a respective vertebra which is spanned by the plate. There is no locking screw associated with these intermediate bone screws to lock the bone screws to the plate.
• The Codman Shurtleff plating system utilizes the side of a preinstalled rivet having a head rotatable to press against the side of the head of a bone screw so as to secure that one screw to the plate. The plates of this system also are provided with holes for receiving intermediate screws, but these screws are not associated with any locking means.
• While the designers of the last-mentioned systems recognized the importance of locking the bone screws in position on their associated plates, they did not provide for any locking of the intermediate bone screws in their associated holes.
• In an earlier version of the Codman Shurtleff system, the locking mechanism was a lever pivotable about a shaft passing entirely through the plate and then flared so as to retain the shaft within the plate. The lever was rotated after the bone screw had been inserted to engage the head of the bone screw and thus secure the bone screw to the plate.
• Based on a consideration of the features of all of the known cervical plating systems, it appears that there remains a need for an improved system having the following combination of features:
• • 1) The plate should be sufficiently strong to perform its intended function without mechanical failure;
  • 2) The plate should be preformed in three dimensions so as to anatomically conform in both the longitudinal and transverse planes to the anterior cervical spine;
  • 3) The plate should be constructed so that all of the bone screws are generally perpendicular to the plate when viewed from the side, but pairs of screws are highly convergent corresponding to any vertebral level when viewed from the bottom, or on end;
  • 4) Each pair of screws engages in a respective vertebra and the high convergence of screws in a pair allows the length of the screws which engage the bone to be longer and still remain within that vertebra and provide a safer and stronger engagement with the vertebrae;
  • 5) The system should include bone screws which are capable of achieving enhanced purchase within the bone of the vertebral body and without the need to penetrate the posterior vertebral cortex and enter the spinal canal;
  • 6) Use should be made of a screw which is self-tapping, thereby eliminating the need for separate tapping steps;
  • 7) A reliable means should be provided for engaging and manipulating the plate during installation;
  • 8) The plate should be engageable with an instrument means which can reliably produce bone screw holes which are coaxial with the screw holes in the plate;
  • 9) It should be possible to prepare the vertebral bone to receive the bone screws so as to produce a stronger connection and a reduced danger of thread stripping by means of a pilot hole punch creating a pilot hole for the bone screws;
  • 10) Alternatively to the use of a pilot hole punch, a relatively (compared to the overall root diameter of the screw) small diameter drill may be used to create the pilot hole.
  • 11) Means should be provided for locking each and every bone screw in position relative to the plate, and the locking means should be of sufficient size and strength to reliably perform its intended functions;
  • 12) Bone screw locking means should preferably be retainable by the plate prior to bone screw insertion, or should be reliably attachable to a driver to prevent any small parts from becoming loose in the wound; and
  • 13) The system should be capable of effecting compression of the vertebral segments to be fused while maintaining and/or restoring lordosis.
OBJECTS OF THE INVENTION
• It is an object of the present invention to provide an improved anterior cervical plating system, installation instrumentation, and installation method which has the above described features and which avoids many of the shortcomings of previously known systems.
• One object of the present invention is to provide a locking mechanism where a plurality of bone screws used for attaching the plate to the vertebrae can be easily and reliably locked in place at the same time by a single operation.
• Another object of the present invention is to provide a vertebral plate in which the locking mechanisms for locking the bone screws may be pre-installed by the manufacturer prior to the insertion of the bone screws by the physician so that the physician does not have to attach the locking mechanism to the plate as a separate procedure during the operation.
• Another object of the invention is to provide an anterior cervical plating system which allows for the intersegmental compression of the spinal segment (compression of the adjacent vertebrae and the fusion graft in the disc space between the adjacent vertebrae) in lordosis, and similarly, where desired, multisegmental compression.
• A further object of the invention is to provide bone screws which provide for tactile feedback to the surgeon to assure sufficient tightening of the screws while avoiding stripping and are less prone to failure by breakage or by loosening.
• Another object of the invention is to provide bone screws which achieve optimal purchase within the bone, without the need to penetrate the posterior cortex of the vertebrae.
• A further object of the invention is to provide plates which are textured or otherwise treated to promote bone growth from vertebrae to vertebra beneath the plate.
• Another object of the invention is to provide a plate which is constructed to reliably engage an instrument for forming all bone screw holes coaxial with the holes formed in the plate, the instrument having integral depth limiting means which completely eliminates the danger of perforation of the posterior vertebral wall or entry into the spinal canal.
• Yet another object of the invention is to provide a system in which the bone screws and locking mechanisms, when fully installed, have a low profile.
• It is another object of the present invention to provide for an anterior cervical plating system which is at least in part bioresorbable.
• It is another object of the present invention to provide for an anterior cervical plating system comprising at least in part of bone ingrowth materials and surfaces.
• It is another object of the present invention to provide for an anterior cervical plating system comprising at least in part of bone growth promoting substances.
• It is another object of the present invention to provide instruments for reliably and easily performing the installation of the plates of the present invention.
• It is still another object of the present invention to provide an improved method of installing the plates of the present invention.
• The above and other objects and features of the invention will become more readily apparent from the following description of preferred embodiments of the invention, provided with reference to the accompanying drawings, which illustrate embodiments of the invention solely by way of non-limiting example.
SUMMARY OF THE INVENTION
• The plating system of the first preferred embodiment of the present invention comprises a plate having a length sufficient to span a disc space and to overlap, at least in part, at least two adjacent cervical vertebrae, a substantial portion of the lower surface of the plate preferably being biconcave, that is concave curved along a substantial portion of the longitudinal axis of the plate and concave curved along a substantial portion of the transverse axis of the plate. The lower surface of the plate may also textured and/or treated to induce bone growth along the lower surface of the plate which contacts the cervical vertebrae. The plate is provided with a plurality of bone screw receiving holes which extend through the plate, from the upper surface to the lower surface of the plate, and at least one locking element is associated with the bone screw receiving hole. The plate and its component parts, may be made of any implant quality material suitable for use in the human body, and the plate and associated component may be made of a bioresorbable material.
• Bone screws are each insertable into a respective bone screw receiving hole for attaching the plate to a vertebra. A locking element, is engageable to a locking element receiving recess and has a head formed to lock the bone screws to the plate. In the preferred embodiment, a single locking element locks a number of different bone screws in place. The locking elements are pre-installed prior to use by the surgeon in a manner so as to not impede installation of the bone screws.
• As a result, the problems previously associated with the locking screws of the type applied after the insertion of the bone screws, including the problems of instrumentation to position and deliver to the plate the locking means, backing out, breakage, stripping and misthreading associated with the prior art more delicate locking screws resembling “watchmaker's parts”, are eliminated.
• In an alternative embodiment of the present invention, a locking element fits within a respective bone screw receiving hole to lock a respective one of the bone screws in place. According to this second embodiment of the invention, each of the bone screws is locked to the plate by means of an individual locking element which bears against at least a portion of the bone screw. Since no other holes need be formed in the plate to attach the locks to the plate, the plate remains quite strong.
• The locking elements can be in many forms to achieve their intended purpose, such as, but not limited to, screws, threaded caps, rivets, set screws, projecting elements, and the like.
• Also, a novel bone screw is disclosed so as to prevent pulling out of the bone screw during use. This is achieved by a design which includes a screw in which the outer diameter or crest diameter of the thread is maintained substantially constant along the entire length of the shaft of the bone screw, from below the head to above the tip, where threads of a lesser outer diameter facilitate insertion. The screw tip is fluted at its distal end to be self-tapping. The thread also has an extremely thin and sharp profile to cut into and preserve the integrity of the vertebral bone stock.
• The plating system does not require that the head of the bone screw be hollow, or that additional holes be placed through the plate in addition to those provided for the passage of the bone screws. It will be appreciated that bone screws are weakened when their heads are hollow and that plates are weakened when they are provided with additional holes.
• Additionally, the plate of the disclosed systems permit the proper aligning of the holes in the plate for the bone screws and for the plate to be easily applied to the vertebrae in compression. The plates include appropriate slots and engagement means for engaging compression instrumentation, described in detail below, for applying a compression force between adjacent vertebrae to which the plate is attached, in a reliable and easy manner.
• An improved locking screw driver is provided. The driver provides for a wedged interference fit with a recess in the head of the bone screws and the head of the locking elements. The same driver is usable for both bone screws and locking elements. The driver ensures that the locking element cannot fall off the driver and become lost in the wound. The driver has a tapered end to facilitate insertion into the complimentary recess in the head of the screws and is used to engage and pick up the locking elements. Alternatively, the receiving socket can be tapered to the same purpose.
• Alternatively, a combination bone screw and locking screw driver is disclosed in which the bone screw driver passes through a longitudinal opening in the locking screw driver so that both the bone screw and the locking screw can be loaded prior to insertion of the bone screw and both can be tightened with one instrument, without removing it from position.
• Also, instruments are provided for forming pilot holes to assist in the ease and accuracy of the installment of the bone screws, and for creating a creating a compression force between adjacent vertebrae during installation of the plate and for holding the plate during installation.
BRIEF DESCRIPTION OF THE DRAWINGS
• FIG. 1 is a top perspective view of a first embodiment of a cervical spine multiple locking plate.
• FIG. 2 is a top plan view of the cervical spine multiple locking plate shown inFIG. 1.
• FIG. 3 is a side elevational view of the cervical spine multiple locking plate shown inFIG. 1.
• FIG. 4 is an end view of the cervical spine multiple locking plate shown inFIG. 1.
• FIG. 5 is a bottom plan view of the cervical spine multiple locking plate shown inFIG. 1.
• FIG. 6 is a top plan view of the cervical spine multiple locking plate shown inFIGS. 1-5, with locking elements installed in an open configuration.
• FIG. 7 is a top plan view of a modification of the plate ofFIGS. 1-6 with a four bone screw locking element in place.
• FIG. 8 is a top plan view of a further embodiment of a cervical locking plate ofFIG. 1 with an elongated central slot for increased compression capability.
• FIG. 9 is a top plan view of a locking element for use with the plates ofFIGS. 1-6.
• FIG. 10 is a top plan view of a locking element for use with the central opening of the plate ofFIGS. 7 and 22.
• FIG. 11 is a top plan view of a locking cap for use in the end openings shown inFIGS. 1, 6, and7.
• FIG. 12 is a side elevational view of the locking element ofFIG. 16.
• FIG. 13 is a side elevational view of another embodiment of the locking element ofFIG. 16.
• FIG. 14 is a top perspective view of an alternative embodiment of cervical spine multiple locking plate for use with locking rivets.
• FIG. 15 is a bottom plan view of the cervical spine multiple locking plate ofFIG. 14.
• FIG. 16 is a top plan view of a two bone screw locking element.
• FIG. 17 is a top plan view of an alternative embodiment of a four bone screw locking element having head slits for increased flexibility of the locking tabs.
• FIG. 18 is a bottom plan view of a rivet type locking element for use with the central opening of the plate ofFIG. 14.
• FIG. 19 is a side elevational view of a rivet locking element.
• FIG. 20 is a top perspective view of the bottom portion of the head of rivet ofFIG. 19 viewed along lines20-20.
• FIG. 21 is a top perspective view of the head portion of a three bone screw locking element.
• FIG. 22 is a top perspective view of a third embodiment of a cervical spine multiple locking plate utilizing locking elements in the form of threaded caps.
• FIG. 23 is a side elevational view of a locking element for use with the plate ofFIG. 22.
• FIG. 24A is a side elevational view of a bone screw in accordance with the present invention.
• FIG. 24B is an enlarged side elevational view of the bone screw ofFIG. 24A.
• FIG. 25 is a side elevational view of an alternative embodiment of a bone screw in accordance with the present invention.
• FIG. 26 is a bottom end view of the bone screw shown inFIG. 24A.
• FIG. 27 is a top end view of the bone screw shown inFIG. 24A.
• FIG. 28 is a top perspective view of a fourth embodiment of a cervical spine multiple locking plate.
• FIG. 29 is a top perspective view of a locking element for use with the plate ofFIG. 28.
• FIG. 30 is a partial side sectional view of the plate ofFIG. 28 along lines30-30 with a bone screw in place.
• FIG. 31 is a top perspective view of the plate ofFIG. 1 positioned against the anterior aspect of three successive vertebral bodies in the cervical spine, a plate holder, and an instrument for forming bone screw receiving holes in to the vertebral bodies.
• FIG. 32 is a cross-sectional view of a portion of the bone forming device shown inFIG. 31 viewed along lines32-32.
• FIG. 33 is a side elevational view in partial cross section illustrating a compression post tool and a compression post engaged to it for insertion into a vertebral body.
• FIG. 34 is a side elevational view in partial cross section of the compression post tool engaged for removal of the compression post from the vertebral body.
• FIG. 35 is a bottom end view of the compression post tool ofFIG. 34.
• FIG. 36 is a side elevational view of a plate engaging hook for use with the compression apparatus shown inFIG. 38.
• FIG. 37 is a cross-sectional view through the plate of an alternative embodiment of a hole forming instrument in the form of a drill guide and drill for use during the plate installation procedure.
• FIG. 38 is a side elevational view showing intersegmental compression of the spine and compression apparatus.
• FIG. 39 is a view similar to that ofFIG. 38 showing the compression apparatus in a further stage of the plate installation procedure.
• FIG. 40 is a top perspective view showing the locking of the bone screws to the plate.
• FIG. 41 is a partial side sectional view of a locking element attached to a driver instrument.
• FIG. 42 is a partial side sectional view of another embodiment of the locking element attached to a driver instrument.
• FIG. 43 is a partial cross-sectional view showing a cervical plate, locking element, and bone screws along lines43-43 ofFIG. 40.
• FIG. 44 is an enlarged portion of detail alongline44 ofFIG. 43.
• FIG. 45 is a side view in partial cross section of a plate holder attached to a plate.
• FIG. 46 is a side view in partial cross section of another embodiment of a plate holder attached to a plate.
• FIG. 47 is a top perspective view of a first embodiment of a single locking plate.
• FIG. 48 is a top plan view of the plate shown inFIG. 47.
• FIG. 49 is a side elevational view of the plate shown inFIG. 47.
• FIG. 50 is an end view of the plate shown inFIG. 47.
• FIG. 51 is a bottom plan view of the plate shown inFIG. 47.
• FIG. 52 is a top plan view of the plate shown inFIG. 47, with locking elements in place.
• FIG. 53 is a side elevational view of a bone screw used with the plate shown inFIG. 47.
• FIG. 54 is a top end view of the bone screw shown inFIG. 53.
• FIG. 55 is a bottom end view of the bone screw ofFIG. 53.
• FIG. 56 is a top plan view of a locking cap for use with the single locking plate ofFIG. 47.
• FIG. 57 is a side elevational view of the locking cap shown inFIG. 56.
• FIG. 58 is a bottom plan view of the locking cap shown inFIGS. 56 and 57.
• FIG. 59 is a bottom perspective view of the locking cap ofFIGS. 56-58.
• FIG. 60 is a top perspective view of the single locking plate ofFIG. 47 shown being held by a plate holder against three vertebral bodies, with the hole forming instrument for punching a pilot hole into the vertebral bodies for receiving a bone screw.
• FIG. 61 is a side elevational view in partial cutaway of the hole forming instrument threaded to a bone screw receiving hole.
• FIG. 62 is a perspective side sectional view of the drill and drill guide threadably engaged to the plate for drilling a hole for insertion of a bone screw.
• FIG. 63 is a top perspective view of a single locking plate installed along a segment of the spine with two locking caps installed in two bone screw receiving holes.
• FIG. 64 is a side elevational view in partial cross section of a locking cap engaged to a driver for installing the locking cap.
• FIG. 65 is a partial cross sectional view of the plate, bone screws and locking caps along line65-65 ofFIG. 63.
• FIG. 66 is an enlarged fragmentary view ofarea66 ofFIG. 65.
• FIG. 67 is a perspective view of a cervical locking plate being held by an alternative plate holder instrument.
• FIG. 68 is an end sectional view showing the plate holder ofFIG. 67 engaging a plate.
• FIG. 69A is an end sectional view of an alternative embodiment of the plate holder.
• FIG. 69B is an end sectional view of another alternative embodiment of the plate holder.
• FIG. 70 is a plate holder instrument with an offset and removable handle.
• FIG. 71 is a top perspective view of a second embodiment of a cervical single locking plate having individual locking elements to lock each bone screw.
• FIG. 72 is a top perspective view of a threaded locking element for use with the cervical single locking plate ofFIG. 71
• FIG. 73 is a partial side sectional view of the plate ofFIG. 71 viewed along lines73-73 with the locking element ofFIG. 72 in place to hold a bone screw, but not fully tightened.
• FIG. 74 is a top perspective view of an alternative locking element for use with a first modification of the cervical single locking plate ofFIG. 71.
• FIG. 75 is a side sectional view of the first modification of the plate ofFIG. 71 with the locking element ofFIG. 74.
• FIG. 76 is a perspective view of an alternative locking element for use with the first modification of the plate ofFIG. 71.
• FIG. 77 is a partial side sectional view of the first modification of the plate ofFIG. 71 with the locking element ofFIG. 76 in place.
• FIG. 78 is a top perspective view of another alternative locking element in the form of a rivet for use with a second modification of the locking plate ofFIG. 71.
• FIG. 79 is a partial side sectional detail view of the plate ofFIG. 71 modified to use a locking element ofFIG. 78 shown in place.
• FIG. 80 is a partial cross sectional view of a plate and bone screw with the end of a tool shown for use in inserting both the bone screws and locking caps.
• FIG. 81 is a side elevational view of another embodiment of the tool ofFIG. 80.
• FIG. 82 is a further embodiment of a cervical spine single locking plate for use in stabilizing multiple segments of the spine.
• FIG. 83 is a further embodiment of a cervical spine multiple locking plate for use in stabilizing multiple segments of the spine.
• FIG. 84A-84E are various embodiments of cervical spine multiple locking plates for use in stabilizing a single segment of the spine.
DETAILED DESCRIPTION OF THE DRAWINGS
• The present invention will be described first in association with the preferred embodiment of the plate system in which a plurality of bone screws are locked in place with one locking element. This is referred to as the multiple locking plate system. The multiple locking plates will be described, then the locking elements for locking the bone screws to the plate, then the bone screws associated with the multiple locking plates, and finally the instrumentation and method of installation of the multiple locking plates. Thereafter the plate systems in which a single locking element locks a single bone screw will be described. This is referred to as the single locking plate system. The locking elements, bone screws, instrumentation, and method of installation associated with the single locking plate will then be discussed.
• 1. Multiple Locking Plate System
• The preferred embodiment of the multiple locking anteriorcervical locking plate2 according to the present invention (here shown by way of example for use in a two level fusion (three adjacent vertebrae)) is shown inFIGS. 1-5.Plate2 has a generally elongated form whose outline generally departs from rectangular due to the presence of lobes orlateral projections4 at the corners and at the center of the sides ofplate2. Eachlobe4 has a rounded outline and contains a respective circular bonescrew receiving hole6. Two additional intermediate circular bonescrew receiving holes8 are located inwardly of the sides ofplate2 and are centered on the longitudinal center line ofplate2.Lobes4give plate2 additional strength in the region surrounding each bonescrew receiving hole6. It is recognized that other shapes for theplate2 may be employed.
• The intermediate paired bonescrew receiving holes8 are for use with a two level (three vertebrae) fusion. The intermediate bonescrew receiving holes8 may be eliminated for a single level (two vertebrae) fusion, or additional intermediate bonescrew receiving holes8 may be added if additional levels are to be fused.
• Plate2 is further provided with three locking element holes12, each of which in the preferred embodiment is internally threaded3, and each of which is surrounded by a shallow countersunkregion14. As will be described in greater detail below, in the preferred embodiment, bone screws are inserted in the bone screw receiving holes and a single pre-installed locking element associated with each of the locking element holes12 locks a number of bone screws30 in position at one time.
• The number of paired bone screw holes generally correspond to the number of vertebrae to be fused. A plate for a one level fusion could have but a singlelocking element hole12, while plates for fusing more than two levels (three vertebrae) could have additional middle locking element holes12 corresponding to additional paired bone screw holes. In the embodiment illustrated inFIGS. 1-6, eachend locking element20 will lock threebone screws30 in place, while the lockingscrew21 in thecentral locking hole12 locks twobone screws30 in place. As shown inFIG. 7,central locking element25 can also be configured so that fourbone screws30 are locked at one time.
• As shown particularly inFIGS. 3, 4 and5,plate2 is shaped so that its bottom surface27 (the surface which will be in contact with the vertebral bodies) has a bi-concave curvature, being concave both in the longitudinal plane (corresponding to its length) and in the plane transverse thereto, corresponding to its width. The concave curvature in the longitudinal plane conforms to the proper shape of the anterior aspect of the spine with the vertebrae aligned in appropriate lordosis. That longitudinal curve is an arc along the circumference of a circle (referred to herein as the “radius of curvature”) 15.0 cm to 30.0 cm in radius and more preferably 20.0-25.0 cm in radius. Viewed on end inFIG. 4, theplate2 has a radius of curvature of a circle 15-25 mm in radius, but preferably 19-21 mm in radius. While theplate2 may have a thickness between 2 to 3 mm, a thickness of between 2.25 and 2.5 mm is preferred.
• Having thebottom surface27 ofplate2 contoured so that it is able to lie flush against the associated vertebral bodies is in contrast to conventional plates which have larger radii of curvature that contact the vertebral bodies only along the longitudinal centerline of the plate, thereby permitting side-to-side rocking of the plate relative to the vertebral bodies. The contour of the plate of the present invention provides effective resistance to rocking of theplate2 relative to the vertebral bodies about the longitudinal center line of the plate, thereby reducing stress on theplate2 and bone screws30, and preventing the soft tissues from becoming engaged beneath the plate.
• Other advantages produced by the above curvature are that theplate2 will conform more closely to the facing bone surface; theplate2 will project from the spine by a smaller distance; soft tissue will be prevented from sliding underneath the edges of theplate2, where it could be subject to damage; and the angle of the bone screws30, perpendicular to the plate when viewed from the side, when installed will be at a substantial converging angle, trapping the vertebral bone between the bone screws30, and thus more strongly anchoring the plate to the spine.
• As shown inFIG. 5, thebottom surface27 ofplate2, preferably has a porous, roughened, and/or textured surface layer and may be coated with, impregnated with, or comprise of fusion promoting substances (such as bone morphogenetic proteins) so as to encourage the growth of bone along the underside of theplate2 from vertebrae to vertebrae. Thetextured bottom surface27 also provides a medium for retaining fusion promoting substances with which thebottom surface27 layer can be impregnated prior to installation. Thebottom surface27 ofplate2 may be given the desired porous textured form by rough blasting or any other conventional technology, such as etching, plasma spraying, sintering, and casting for example. If porous, thebottom surface27 is formed to have a porosity or pore size in the order of 50-500 microns, and preferably 100-300 microns. Fusion promoting substances with which the porous,textured bottom surface27 can be impregnated include, but are not limited to, bone morphogenetic proteins, hydroxyapatite, or hydroxyapatite tricalcium phosphate. Theplate2 may comprise of at least in part a resorbable material which can further be impregnated with the bone growth material so that as theplate2 is resorbed by the body of the patient, the bone growth material is released, thus acting as a time release mechanism. Having theplate2 being made from a material that is resorbable and having bone growth promoting material present permits the vertebrae to be fused in a more natural manner as the plate becomes progressively less load bearing thereby avoiding late stress shielding of the spine.
• As further shown inFIGS. 4 and 5, at least one end ofplate2 has arecess18 that can cooperate with a compression apparatus, described in detail later in reference toFIGS. 36 and 38.
• FIG. 6 is a top plan view of theplate2 ofFIG. 1 with lockingelements20,21 inserted into the locking element receiving holes. In the preferred embodiment, the lockingelements20,21 are in the form of screws that cooperate with the threadedinterior3 of the locking holes12. Each of these lockingelements20,21 is shown in its initial open orientation, where the orientation of thecutouts22 in thehead23 of each lockingelement20,21 is oriented so as to permit introduction of bone screws30 into adjacent bonescrew receiving holes6,8 without interference by thehead23 of the lockingelement20,21. It is appreciated that other configurations of thehead23 are possible so as to permit introduction of bone screw into adjacent bone screw receiving holes without interference by thehead23.
• FIG. 8 is a top view of another embodiment ofplate2 ofFIGS. 1-5, and is generally referred to asplate120.Plate120 is provided with a longitudinally extendingelongated slot122 along its longitudinal axis which is superimposed on themiddle locking hole12.Elongated slot122 allows additional relative movement betweenplate120 and acompression post54 associated with a compression tool during the compression procedure, as discussed below.
• Referring toFIGS. 14 and 15, an alternative embodiment of a multiple locking plate referred to by thenumber70 is shown. Inplate70, rather than the threadedlocking hole12, acentral opening200 for receiving aremovable rivet202, of the type shown inFIGS. 17-20, is provided.FIG. 15 is a bottom plan view of theplate70 shown inFIG. 14. The contour of theplate70 is the same as that of theplate2 shown inFIGS. 1-5. Therivet202 is removable and fits within the unthreadedopening200, comparable to the lockinghole12 andslot122 described above. Other embodiments may employ a rivet that is not removable, but is manufactured as part of theplate70 as would be used in the end locking holes19 ofFIGS. 14 and 15.
• Referring toFIG. 22, another alternative embodiment of a multiple locking plate is shown and is generally referred to by thenumber230. Theplate230 uses threaded caps, such ascap300 shown inFIGS. 9 and 23, for a locking element or preferably one with cut outs as described having an appearance in a top view such as the locking element inFIGS. 10-11, for example. Thecentral locking hole232 has an elongatedslot234 for providing an increased compression capability, as will be discussed further herein.
• Referring toFIGS. 10-13, a first embodiment of a lockingelement20,21,25 in the form of locking screws according to the present invention for use withplate2 is shown.FIG. 10 is a top plan view which illustrates thehead23 of thecentral locking element25 shown inFIG. 7. Theshaft46 of lockingelement25 is threaded47 to mate with the threading3 within the associated lockinghole12 ofplate2. As shown inFIG. 21, eachsegment49 on each side ofcutouts22 of the lockingelement21 has a bearingsurface48 formed at the lower surface of lockingelement head23. As shown inFIG. 16, the lockingelement head23 can be provided with twoslots42 for providing flexibility to thelocking element head23 to assist in the locking element's ability to ride over the top of thebone screw head32 during the bearing action when the locking element is rotated. Alternatively, it is appreciated that the bearing surface can be cammed, ramped or wedged. The cammed, ramped or wedged features can also be used with the other locking elements described herein.
• Referring toFIGS. 6 and 10-13, it will be appreciated that when the lockingelements20,21 are rotated in the clockwise direction with respect to the view ofFIG. 6, a respective bearing surface48 (as best seen inFIG. 21) will ride upon the curvedtop surface39 of a respectivebone screw head32 in order to positively lock the associated bone screws30 and thelocking elements20,21 in place.
• Alternatively, as shown inFIGS. 12 and 13 in place of a bearingsurface48, a ramp or wedge shapedsurface44 may be used to increase the force applied to thebone screw head32. When locked, the leading end of the ramped portion of the locking element would be lower than the prominence of thebone screw head32 so that more force is needed to lift the locking element and untighten it than is needed for the locking element to remain tight and locked. However, the locking element heads23 need not have slots, be cammed, or have a ramped surface to achieve the locking of thebone screw30 in place. Pressure, friction, interference fits, or other engagement means capable of preventing the locking element from moving from its locked position may be employed.
• Therivet202, shown inFIGS. 17-20 is intended for use in association withplate70 shown inFIGS. 14-15, is shown in detail in cross section inFIGS. 19 and 20. Therivet202 has ahead204, ashaft206, and anelongated bottom segment208 for fitting within thecorresponding opening200 in theplate70. Thelower surface210 of thehead204 of therivet202 has an irregular surface which may be cammed, such as on the bottom of lockingelement20,21, for engaging thetop surface39 of thebone screw head32. For use in the end locking holes19, the upper surface of theelongated bottom segment208 can have an irregular surface for cooperating with the irregular surface of the bottom of theplate70 to hold therivet202 in the locked position against thebone screw head32, as shown inFIG. 15. While the rivet ofFIG. 18 is a separate, removable component from the plate, the rivets, and particularly those for use with the end locking holes, can be formed as part of the plate during the manufacturing process of the plate and rivet can be non-removable.
• Each of the above embodiments provides tight attachment of the locking element relative thebone screw30 and relevant plate.
• In the alternative embodiment of multiple lockingplate23 shown inFIG. 22, the locking element can be in the form of threadedlocking cap300 shown inFIG. 23. The threadedlocking cap300 has athread302 on its outer circumference corresponding to thethread303 on the inner circumference of the lockingelement depressions304 in the top of theplate230 shown inFIG. 22. The lockingcap300 is relatively thin, particularly compared to its width. The top305 of lockingcap300 is provided with a noncircular throughhole306 for receiving a similarly configured driving tool.
• Referring toFIGS. 28, 29, and30 another embodiment of the multiple locking plate generally referred to by thenumber400 and a locking element in the form of athin locking member412 are shown.Plate400 has an opening in its top surface for insertion of thethin locking member412, arecess402 associated with each of the bonescrew receiving holes408 and aslot410 in the side wall of the bonescrew receiving holes408 to permit thethin locking member412, having a series of thin projections orblades414, thinner than theslot410, that give this lockingmember412 an appearance similar to that of a propeller. Thethin locking member412 is able to be rotated within the plate so as to not cover the bone screw holes, thus allowing thethin locking member412 to be pre-installed prior to the installation of the bone screws by the surgeon. Limited rotation of thethin locking member412 allows theblades414 to protrude through theslot410 and to cover a portion of the top of the associated bone screws30. Theblades414 of thethin locking member412 are flexible and, when rotated, slide over thetop surface39 of thebone screw head32 to lock thebone screw30 in place. As with the other embodiments discussed, each of the embodiments of the locking element is capable of locking more than onebone screw30. It is appreciated that the various multiple locking plates and locking element combinations are capable of locking as many as four bone screws at once, but are equally effective for locking a lesser number or none at all, that is securing itself to the plate.
• It will be noted that one characteristic of each of the above described locking element embodiments is to have a driver engagement means, in these cases for example, arecess24 as large as therecess34 in the bone screws30 so that the same tool can be used to turn both the bone screws30 and the locking elements. Also, the locking elements are sufficiently strong and have sufficient mass so as to be able to withstand being locked without breakage.
• All of the shown examples of the multiple locking elements that have a number of cutout portions have an arc with a radius greater than that of the bone screw head. In addition, thehead23 of each lockingelement20,21 is provided at its center with anoncircular recess24, such as shown inFIG. 9 which is engageable by an appropriate manipulation tool, such as shown inFIGS. 40-42. In the embodiment ofhead23 shown inFIG. 9, the associated tool would have a hex head, but as discussed with regard toFIGS. 80 and 81, other shapes of recesses in thehead23 may be used. The thread of each lockinghole12 and of each lockingelement20,21 has a close tolerance so that they will reliably retain their orientations so as to permit introduction of bone screws30 into bonescrew receiving holes6,8 without interference.
• It is appreciated that while various forms of locking elements have been disclosed, in light of the teaching, other equivalent means can be used for the purpose of locking the bone screws30 in place. InFIG. 83, an alternativemultiple locking plate990 is shown having additional intermediate bonescrew receiving holes980 and associated lockingelements960 for locking bone screws30 in place.Plate990 allows for a more close spacing and more pairs of bone screw holes than the number of vertebrae to be engaged.
• InFIGS. 84A-84E various plates700a-gused for a single level fusion are shown. Each of these plates700a-gis designed to span one spinal segment consisting of one disc space and two adjacent vertebrae (containing the bone graft), and have bone screws inserted into the end of the vertebrae through the bonescrew receiving holes6 associated with the two adjacent vertebrae and then locked in place. As shown inFIGS. 84A-84E, one locking element710, or two locking elements can be used to lock four bone screws in place. InFIGS. 84A-84E, each of the plates700a-eis shown with the locking elements in their open orientation, before being rotated to lock the bone screws.
• Each of the above described plates can have the same generally biconcave contour as already described for conforming to the anterior aspect of the spine.
• FIGS. 24A and 24B provide a side view of one embodiment of abone screw30 according to the present invention.FIG. 27 is a top view of thebone screw30. At the center ofbone screw head32 is a profiledrecess34 which may have the same form as therecess24 of each lockingelement20,21 in which case it may be turned with the same tool as that employed for turninglocking elements20,21. It is appreciated that the driver engaging portion of thebone screw30 could be slotted, and be either male or female (as is shown).
• In the embodiment ofbone screw30 shown inFIGS. 24A and 24B, thebone screw head32 is stepped, with the firstlower head portion35 being contiguous with thescrew shank33 and has a smaller diameter than the upper portion of thebone screw head32. When this embodiment ofbone screw30 is employed, each bonescrew receiving hole6,8 of theplate2 has a countersunkregion14 matching the diameter of the upper portion of thebone screw head32 and dimensioned for an interference fit. Thelower portion35 of thebone screw head32 is dimensioned to achieve an interference fit with its associated portion of bonescrew receiving holes6,8. The larger diameter upper portion ofbone screw head32 assures that thebone screw30 cannot be advanced completely through bonescrew receiving holes6,8 ofplate2. Thebone screw30 passes completely through the upper surface of theplate2 without engaging the upper surface in any way.
• As shown inFIG. 44, thehead32 ofscrew30 passes unobstructed through the upper surface of the plate until the lower surface ofenlarged screw head32 engages the upper face of the narrowed bone screw receiving portion at the midsubstance or below the midsubstance of the plate. This is considered optimal for allowing for the greatest screw to plate stability, even absent the lock, against all forces except those reverse the path of insertion, while still providing for the greatest plate strength beneath thebone screw head23. That is, since the plate is of only generally 2-3 mm in thickness, a sheer vertical circumferential wall is best able to constrain the motion of a screw if the head is similarly configured and there is little tolerance between them. Placing the support of the head near the mid thickness of the plate is preferred as it allows the head to remain large to accommodate the recess for the driver without being weakened, while placing the support of the head away from the upper surface of the plate allows the screw head to be deep into the plate. Placing the support of the head at approximately the mid thickness of the plate assures plenty of plate material beneath the head to support while providing adequate head length above and below the contact point to prevent the contact point from acting as a fulcrum by providing adequate lever arms to prevent unwanted motion.
• In the alternative embodiment ofbone screw30′, as shown inFIG. 25,bone screw head32′ is tapered in the direction from the top of thebone screw head32′ towardscrew tip36′. Again, thebone screw head32′ is dimensioned to achieve an interference fit in the associated bonescrew receiving hole6,8 when thebone screw30′ has been fully installed. When this embodiment ofbone screw30′ is employed, bonescrew receiving holes6,8 need not be provided with a countersunkregion4.
• In each of the above embodiments of the bone screws, the bone screws30 and30′ present a unique combination of a taperedscrew shaft33 and ahelical thread31. The diameter ofscrew shaft33 generally increases from a distal portion of the shaft near thescrew tip36 toward the proximal portion of the shaft nearscrew head32. In the preferred embodiment, the rate of increase in diameter is also greater near thebone screw head32. Such a shape avoids stress risers and provides increased strength at the screw-plate junction, where it is needed the most. The tapering ofscrew shaft33 may have a concave form, as shown inFIG. 24A, or may be linear. The distal portion of thescrew shaft33 may assume a constant diameter.
• Referring again toFIGS. 24A and 24B, thethread31 of thebone screw30 has a substantially constant outer, or crest, diameter “d” from the proximal portion of the shaft below thebone screw head32 to the distal portion of the shaft near thebone screw tip36. In thescrew tip36, the crest diameter ofthread31 may be reduced for preferably one to two turns to facilitate the insertion and penetration of thebone screw30 into the bone.
• In the preferred embodiment, thethread31 of eachbone screw30 has an outer diameter slightly smaller than the diameter of thelowest portion35 of thebone screw head32, which is adjacent the trailing, or upper, end of the associatedthread31. In addition, thethread31 is relatively thin, in the direction of the longitudinal axis of the screw, and tapers outwardly, and has a cross section of a triangle.
• An example of the dimensions of a bone screw for use in human anterior cervical spinal surgery for insertion into the vertebrae is as follows: the threaded portion of said screw has a length from about 10 mm to about 22 mm (12-18 mm preferred) and a head length from about 1 mm to about 3 mm (2-2.5 mm preferred). The threaded portion should have a maximum outside diameter from about 3.6 mm to about 5.2 mm (3.8-4.5 mm preferred) and the head has a diameter from about 3.8 mm to about 6 mm (4-5.5 mm preferred). The thread pitch is from about 1.25 mm to about 2.5 mm (1.5-2.0 mm preferred) and has a sharp and thin threaded profile. The apex of the two faces of the thread have an angle of less than about 21 degrees (15 degrees preferred) and the base of the thread is less than about 0.60 mm thick (0.25 mm-0.35 mm preferred). The screw has a root diameter that increases from proximately above the tip of the shank, along the longitudinal axis to proximately below the head portion of the screw. Preferably, the tip of the screw tip is fluted by at least one cut out section so as to make the screw self-tapping.
• Even though thethread31 of thebone screw30 has a thin profile, the thread will nevertheless be stronger than the bone into which it is introduced so that this thread will efficiently cut a thin helical groove in the bone tissue. The volume of bone that will be displaced by the thickness of the thread is minimized by the thin form of the thread, yet the substantial crest diameter of the screw thread maximizes the surface area of the threads in contact with the bone. While enlarging thescrew shaft33 diameter near thebone screw head32 increases its strength where needed, reducing thescrew shaft33 diameter away from thebone screw head32 where such strength is not required allows for the maximum area of engagement for thethread31 to the bone.
• In the preferred embodiment, as shown inFIGS. 24A and 26,bone screw tip36 is provided with cuttingflutes38, to make thebone screw30 self-tapping. Unlike the prior art bone screws, used for anterior cervical spinal surgery which are not self-tapping, the thread form of the present invention screw is itself more like a tap than a conventional screw in that the threads are very sharp and fluted. Additional embodiments of the bone screws30 is shown inFIGS. 53-55.
• By way of example, plates for fusing three adjacent vertebrae (2 interspaces, or two spinal segments) are shown. Each set of the bone screw receiving holes associated with a vertebrae is considered to be a segment of the plate so that for example, inFIG. 1 three segments are shown—an upper, a central, and a lower segment. While the present discussion is in association with plates for use in fusing three vertebrae across two interspaces, it should be understood that longer and shorter plates having the appropriate number and location of bone screw receiving holes corresponding to the number of vertebrae to be fused are contemplated, and would take the form of the plates shown with fewer or more intermediate segments, such as the segment alongline9 ofFIG. 1, or the intermediate segments of the plates shown inFIGS. 82-84F.
• Referring toFIGS. 31-42, an outline of the steps of the method for installing the plates of the present invention is set forth below. A detailed description of the instrumentation and method for installing the plates of the present invention follows the outline.
• Step 1
• Having completed the interbody fusions, the surgeon removes any bone spurs or localized irregularities along the front of the spine of the area to be fused.
• Step 2
• The correct length plate is selected by the surgeon by measuring the distance on the spine by a caliper, ruler, template, and the like. That plate having a length sufficient to span the distance of the spine to be fused and to partially overlap a portion of each of the end vertebrae to be fused.
• Step 3
• Utilizing a plate holder, the plate is placed into the wound and positioned to confirm positioning, length, and screw hole alignment relative to the segments of the spine to be fused.
• Step 4
• As shown inFIG. 31, with the plate thus positioned and securely held, the plate may be attached to any of the vertebrae to be fused (by example only, here shown as the top vertebra).
• Sub-Step 4A
• The pilot (guide)hole punch60 is attached to theplate2 as perFIG. 32, or alternatively, while not preferred the drill guide may be used as perFIG. 37. In either event, the pilot hole forming means rigidly aligns with and is captured by the plate bone screw receiving hole wall.
• Sub-Step 4B
• The pilot hole is then formed by impacting the pilot hole punch ofFIG. 32 or drilling with the drill ofFIG. 37. In the alternative while not preferred, the formation of the pilot hole can be done away with altogether and the correct screw selected so as to have a length less than the distance along its path to the posterior vertebral cortex can be directly inserted.
• The determination of the appropriate screw length is made by measuring or templating from radiographs, MRI's, or CT scans, or determined directly by measuring the depth of the disc space.
• Step 5
• The correct screw is then attached to the screw driver which regardless of the specific form of the screw driver engagement means, is designed to have an interference fit so as to remain firmly bound to the driver during transport to the insertion site.FIGS. 41, 42,63,64,80 and81 show various ways of achieving such a fit of the driver and screw. In addition to a wedging at the screw and driver interface, clips, and springs and other means are well known for temporarily and reversibly securing the screw to the driver, such as is shown inFIG. 80 where a slotted inwardly springing sleeve holds a threaded cap peripherally until, as it is screwed into the plate, it is automatically pushed back releasing the threaded cap.
• Once a first bone screw has been fully inserted into a vertebra through the plate, it is preferable to insert the other of the transverse pair in the manner already described as perFIG. 33.
• In a similar manner, it is possible to insert the remaining bone screws as per the surgeon's preference into each of the vertebrae to be included into the fusion, just the end vertebrae of the fusion construct, or additionally place screws into the fusion grafts.
• However, as shown inFIGS. 33, 34,38 and39, it is possible with the present invention at the surgeon's option to place any portion or all of the fusion construct under compression and to do so intersegmentally or across the entire length of the fusion construct even when multi-segmented.
• It is appreciated that the same procedure could be generally used for any of the plate systems of the present invention.
• As shown inFIG. 31, the vertebrae50a-care separated from one another by fusion graft blocks51 which were previously installed in the spinal disc space between adjacent vertebrae50 forming a fusion bone graft construct.Plate2 is shown inFIG. 31 with the lockingelements20,21 removed in order to simplify the illustration. It will be understood, however, that in the preferred embodiment the lockingelements20,21 can be, and preferably are, pre-installed in the positions shown inFIG. 6 prior topositioning plate2 upon vertebral bodies of the vertebrae50, thereby saving the surgeon time and trouble.
• Plate2 may be held in position by any known plate holding means, but preferably by the holding tools shown inFIGS. 45, 46 or70 by thenotches142 in the sides of thecompression arms104,130 of avertebral compressor tool100 shown inFIG. 39, or as a further alternative, by the unitary plate holder similar to theFIG. 70 design.
• As shown inFIG. 45,plate holder870 has a hollowtubular housing872, with acentral rod874 having athread878 at one end for engaging one of the threaded locking holes12 in theplate2. The bottom end of thehousing872 hasprojections880,882 that extend outwardly and then downwardly to fit into the bonescrew receiving holes8 of theplate2 preventing thehousing872 from rotating. Thecentral rod874 is located in thehousing872 such that it can be rotated by rotating a handle (not shown) which is fixed to thecentral rod874 at its upper end.
• InFIG. 46 an alternative embodiment of theplate holder890 is shown. A singlesolid member890 has a threadedprojection894 at its bottom end for attachment to the central threaded lockinghole12 in the plate. The bottom surface of theholder890 of this embodiment is contoured so as to match the contours of the top surface of the plate adjacent to the lockinghole12, shown as a depression14 (FIG. 1).
• Referring toFIGS. 67-68, an embodiment of a plate holder for holding any of the plates while being positioned on the vertebrae is shown and generally referred to by thenumber800. Theplate holder800 has a hollowtubular housing802, with acentral rod804 having ahandle806 at one end and athread808 at its other end for engaging one of the threaded locking holes12 in theplate600. The bottom end of thehousing802 hasprojections810,812 that extend outwardly and then downwardly814,816 to fit along the side edge of theplate2 between the end andintermediate lobes4, preventing thehousing802 from rotating. Thecentral rod804 is located in thehousing802 such that it can be rotated by rotating thehandle806 which is fixed to thecentral rod804 at its upper end. Thiscentral rod804 can also be attached to thehousing802 so that it can move up and down to some extent, by any number of conventional ways, such as by having thecentral rod804 have an annular depression with a length of approximately 3-5 mm, and a set screw projecting inward from the housing to engage thecentral rod804. Once theplate600 is in the proper place and the plate is attached to one of the vertebrae bybone screws30, thecentral rod804 is disconnected from the opening in theplate600 and theholder800 is removed.
• FIG. 69A is an alternative embodiment of theplate holder850. A singlesolid member852 has a threadedprojection854 at its bottom end for attachment to the central threaded lockinghole12 in the plate. Thesolid member852 could also be threaded into a bonescrew receiving hole6. The bottom surface of theholder850 of this embodiment is contoured so as to match the contours of the top surface of the plate adjacent to the lockinghole12, shown as a depression14 (FIG. 1).
• FIG. 69B is another embodiment of theplate holder850′. A housing851′ having anend853′ configured to engage a bonescrew receiving hole6 contains arod855′ having an uneven diameter and having a threadedportion857′. Asrod855′ is rotated by a handle similar to handle806 shown inFIG. 68,rod855′ screws downward into the housing851′ into matchingthreads858′. As the end ofrod855′ is driven down, it spreadsportions859a′ and859b′ (859c′ and859d′ not shown) wedgingplate holder850′ into a bone screw receiving hole of the plate.Plate holder850′ is best used with non-threaded bone screw receiving holes, but works for all types of bone screw receiving holes.
• Referring toFIG. 70, an alternative embodiment of the plate holder referred to by thenumber800′ is shown in which there is aremovable handle860 that is used for first attaching theplate holder800′ to the plate, by rotating theshaft804, and then for holding theplate holder800′ off to the side byextension864, during the attachment procedure reducing the interference of theplate holder800′ with the surgical procedure.
• Referring toFIG. 38, acompression tool100 is shown with atoothed gear bar102 having afirst compression arm104 secured to its free end.Compression arm104 has at its distal end abore106 for removably holding either aplate engaging element108, shown inFIG. 36, having ahook110 at one end for engaging a depression or notch18 in the end ofplate2, or for removably holding acompression post54 shown inFIGS. 33-34. As shown inFIG. 36,plate engaging element108 includes ashaft112 that will be inserted into thecorresponding bore106 ofcompression arm104, and aflange115 for resting against the bottom face ofbore106 to accurately limit the depth of insertion ofplate engaging element108 into thebore106. Aring spring128, preferably of metal, is located in an annular depression of theshaft112, for holding theplate engaging element108 in thebore106.
• Referring toFIGS. 38-39,compression tool100 includes a secondmoveable compression arm130 movable alongtoothed bar102 parallel tofirst compression arm104. The distal end of thesecond compression arm130 also has abore132, the same asbore106, that can receive aremovable compression post54.Bores106 and132 are the same so that eithercompression arm104,130 can be used to hold theremovable compression post54, permitting thecompression tool100 to be used in any orientation. By permitting theplate engaging element108 and thecompression post54 to both rotate and slide in thebores106,132 of the twocompression arms104,130, with theplate engaging hook110 able to work even at an angle to the plate allows for the apparatus to be readily attachable to the spine through thecompression post54 and plate.
• Compression arm130 has a driving assembly consisting of a toothed wheel (not visible) which is engaged with thetooth gear138 of bartoothed gear102 and is connected tocompression arm130 such thatcompression arm130 is movable along the length oftoothed gear bar102 by means of the rotation ofhandle140, which is connected to the toothed wheel. When thehandle140 is turned in the direction of the arrow shown inFIG. 38,compression arm130 is moved towardcompression arm104. The driving assembly has a self lock release mechanism whereby the movement of the twocompression arms104,130 away from one another is prevented, without the activation of the release. On the inward distal end of each compression arm, on facing sides, is anotch142 or recess for holding theplate2 along its sides between thecentral lobes4 andend lobes4, as shown inFIG. 38.
• While thetoothed gear bar102 andcompression arms104,130 have been described as being straight, it is possible that thetoothed gear bar102 andcompression arms104,130 may be arcuately or otherwise shaped, so as to induce lordosis in the vertebrae, if so desired.
• As shown inFIG. 31, in the event that thecompression tool100 is used to hold theplate2, theends144 of thecompression arms104,130 will be located in line with the fusion graft construct51 which was placed in the disc space whenplate2 is properly positioned. A gap will exist betweenplate2 and each fusion graft construct51, providing a space to accommodate the free ends ofarms104,130 should they extend beyond the bottom surface of theplate2. As will be described below, thesame compression tool100 can also be used for compressing a plurality of cervical vertebral bodies with bone grafts interposed during the attachment ofplate2 to the vertebrae50.
• Referring toFIG. 31,plate2 is held by a suitable holder, in this case shown as thecompression arms104 and130. Once theappropriate length plate2 has been properly positioned so that the bonescrew receiving holes6 are aligned with each of the respective vertebrae50a-cto be fused, the next step is the formation of bonescrew receiving holes6 prior to installation of the bone screws30 themselves in thevertebrae50a. While the procedure is described as first attaching theplate2 to theupper vertebrae50a, theplate2 can be attached to any of the vertebrae in any order. Different sized plates are used so that, as indicated above, the physician will select the appropriate sized plate in which the bonescrew receiving holes6,8 are aligned with the threeadjacent vertebrae50a,50band50c. Pilot holes are formed by a pilothole forming apparatus60 shown inFIGS. 31 and 32. Unlike with known prior art and screw plating systems, the bone screws30 may be inserted without the prior formation of an opening into the vertebrae as the bone screws30 are preferably sharp pointed, self-tapping, and have at their tip a diminishing major diameter to assist the screw entering and pulling into the bone. However, while a hole into the bone of the vertebrae may be formed prior to screw insertion, it is preferable that the hole be of a smaller diameter than the root diameter of the screw and for a different purpose than with the prior art. With the prior art the hole drilled had to be of a diameter equal to but preferably larger than the root (minor) diameter of the screw, as the screws were not self-tapping. It is desirous to create pilot holes to assure that a proper path for the bone screws30 is maintained, and also to prevent damage to the vertebral bone during insertion of the bone screws30. In addition, the pilothole forming apparatus60 creates a more compact vertebral bone mass for reception of the self-tappingbone screw30 used in this insertion.
• As shown inFIGS. 31 and 32, pilothole forming apparatus60 includes a hollowcylindrical housing62 having a bottom provided with a throughhole63.Housing62 contains acentral shaft64 which extends through the throughhole63 in the bottom ofhousing62. The leadingend66 ofshaft64 tapers gradually to asharp point65.Shaft64 is provided with aring member78 having a diameter which closely corresponds to the inner diameter ofhousing62 to guide the travel ofshaft64 withinhousing62. Acompression spring67 is interposed between thering member78 and the bottom ofhousing62.Compression spring67 provides a bias force which normally urges thesharp point65 into a retracted position withinhousing62. The upper end ofshaft64 has anenlarged head68 extending outside of thehousing62 which is intended to be manually depressed or struck by a percussion instrument in order to drive thesharp point65 out ofhousing62 and into avertebral body50a.Shaft64 is given a length, taking into account the length thatspring67 will have when fully compressed, to determine the maximum depth of the pilot hole formed in a vertebral body. The depth is selected to assure that the pilot hole does not reach the posterior cortex of the vertebral body, which borders the spinal canal.
• Certain structural features ofhole forming apparatus60 are shown in greater detail inFIG. 32. In particular, it can be seen that the bottom end ofhousing62 has a projectingportion69 dimensioned to fit precisely in a bonescrew receiving hole6 or8 ofplate2. The bottom71 of the projectingportion69 is flat in a plane perpendicular to the axis ofhousing62. When the projectingportion69 ofhousing62 is snugly inserted into a bonescrew receiving hole6,8 and the flat bottom71 is placed flush against the upper surface ofplate2, it is assured that the leadingend66 ofshaft64 will form a pilot hole in the vertebral bone having an axis perpendicular to the plane of the associated portion ofplate2, thereby assuring that thebone screw30 will be subsequently installed so that its axis is also perpendicular to the plane which is parallel to the upper and lower surfaces of the associated portion ofplate2.
• When a plate is used which has a threaded bone screw receiving hole, the lower end of the pilothole forming apparatus60 is threaded so as to engage the thread in the bonescrew receiving hole6,8 thereby fixing the plate and the pilot hole forming apparatus together, assuring a stable fit between the pilot hole forming apparatus and theplate2. It should be noted that the diameter of theleading end66 of theshaft64 is small since it has to fit within the small space left between the inside wall of the pilot hole forming apparatus. Since it is only a pilot hole for a self-tappingbone screw30 that is being formed, the small diameter is satisfactory.
• Referring toFIG. 37, if for any reason it should be desired to form the pilot hole in the vertebral body50 by drilling, rather than by the use of the pilothole forming apparatus60, use can be made of adrill guide80, having a lower end as shown inFIG. 37. Thedrill80 guide consists of atubular member82 and a small diameterlower end84 which is dimensioned to achieve a precise interference fit in the associated bonescrew receiving hole6,8 ofplate2. Along the small diameterlower end84,drill guide80 has an axial end surface in a plane perpendicular to the longitudinal axis of thedrill guide80 so that when thesmall diameter portion84 is fitted into the bonescrew receiving hole6 and the surface surrounding thesmall diameter portion84 is flush against the upper surface ofplate2, the axis of the drill guiding bore86 indrill guide80 will be precisely perpendicular to the upper and lower surfaces of the associated portion ofplate2. As with the case described above, the bottom end of thedrill guide80 can be threaded so as to engage to the threaded opening ofplate2.
• After the bonescrew receiving holes6,8 are formed in thevertebral body50athrough the upper two bonescrew securing holes6 ofplate2 by means of eitherhole forming apparatus60 ordrill guide80, bone screws30 are threaded into the vertebrae50 while holding theplate2 firmly against the vertebrae50 withcompression tool100 orplate holder800. This locks the plate to thevertebrae50a.
• It is then possible, if desired, to compress the fusion graft in the nextadjacent vertebrae50bbefore attaching bone screws30 to theadjacent vertebrae50bthrough the central bone screw receiving holes ofplate2. Once the initial bone screws are in place in thevertebrae50a, theplate holder100 or800 may be removed from theplate2. The compression of the fusion graft construct between the twoadjacent vertebrae50aand50bis achieved as follows:
• Compression post54 is driven through thecentral locking hole12 ofplate2 by means ofinsertion tool90, shown inFIGS. 33, 34 and35, into the vertebral bone ofvertebra50b, where it will be used in a subsequent step to apply a compression force betweenvertebrae50aand50b.Compression post54 consists of ashaft56 having asharp point57 at its lower end, an enlargedcentral collar58 which serves as a depth stop, and acircumferential groove59 proximate its upper end, defining anenlarged head55.
• Compressionpost insertion tool90 consists of ashaft92 having a closedhollow portion94 at itslower end96 for receivingcompression post54 and anenlarged percussion cap98 at its other end. Compressionpost insertion tool90 also includes in its lower end96 asecond opening95 having arecess99 in its inside wall for permitting engagement of theenlarged head55 on thecompression post54 within thedepression97. Thesecond opening95 is in communication with thehollow portion94 of theinsertion tool90, as shown inFIG. 35.
• Referring toFIG. 38, thebore132 in thesecond compression arm130 ofcompression tool100 is then applied overcompression post54 invertebrae50b, and theplate engaging element108 is inserted in thebore106 of thefirst compression arm104 ofcompression tool100. Thehook110 of theplate engaging element108 shown inFIG. 36 is fitted into thenotch18 at the end of theplate2 which is fixed by the bone screws30 inserted into thevertebra50a, as shown inFIG. 38. As indicated above, however, thecompression tool100 can be rotated so that thefirst compression arm104 is now at the bottom and is able to fit over thecompression post54 invertebrae50c.
• Since the plate is attached tovertebrae50aby means of bone screws30 andcompression post54 is fixed to theadjacent vertebrae50b, movement of the first andsecond compression arms104 and130 in the direction ofvertebrae50aby rotation ofhandle140 results in compression of the bone graft construct51 between theadjacent vertebrae50aand50b. The distance of several millimeters is sufficient for compression of thebone graft construct51. Once the desired compression is obtained, bone screw pilot holes can be formed invertebral body50bby means of pilothole forming apparatus60, as described above, for insertion of bone screws30 into bonescrew receiving holes8 ofbone plate2, fixing theplate2 to theadjacent vertebrae50b.Compression tool100 can then be withdrawn by activation of the release.
• FIG. 39 illustrates the use ofcompression tool100 to induce compression between the lower twovertebral bodies50band50cafter bone screws30 have been installed in the middlevertebral body50bas just described. As shown inFIG. 39,compression post54 remains in place in the middlevertebral body50band anadditional compression post54 is driven into the lowervertebral body50cby means of pilothole forming tool60 distal to the plate itself in the recess between theend projections4 to allow for thelower compression post64 to be moved towardsvertebrae50bupwardly as shown. Theoriginal compression post64 is inserted inbore106 in thefirst compression arm104 and theadditional compression post54 is inserted into thebore132 of thesecond compression arm130 ofcompression tool100. Again, as discussed above, the turning of thehandle140 results in the twocompression arms104,130 moving towards one another, resulting in thecompression post54 invertebrae50cmoving towards theupper compression post54 invertebrae50b, once again compressing the fusion graft construct51 betweenvertebrae50band50c. Theupper compression post54 invertebrae50bcan not move since thevertebrae50bhas been fixed to the plate by the insertion of the bone screws30 in the bonescrew receiving holes8 of theplate2. Thus, only thelower compression post54 andvertebrae50ccan move. As before, the pilot holes associated withvertebrae50care formed and the bone screws30 are inserted through bone screw receiving holes6. Thecompression tool100 is then removed.Compression post54 is then extracted from the vertebrae by inserting it in thesecond opening95 of the compression post insertion/removal tool90, so that it engages theenlarged head55 of the end ofcompression post54 bydepression97, as shown inFIG. 34.
• It is recognized that other variations in the order of compression may be employed. For example, during the compression of the fusion graft construct51 betweenvertebrae50band50c, thehook110 ofplate engagement element108 may engage thenotch18 in the end of theplate2, and the other compression arm of thecompression tool100 may engage thecompression post54 in the thirdadjacent vertebrae50c. It should also be noted thatplate2 has a recess end cut out portion between the lobes at the end of the plate for insertion of thecompression post54 in the vertebrae. Otherwise, there may not be room below the end of theplate2 for insertion of thecompression post54.
• It will be noted that the above-described procedure will be performed with the bone screws30 fully inserted intovertebral bodies50a,50band50cand lordosis is maintained during compression of thebone graft construct51.
• As indicated above, the procedure for attaching theplate2 to thevertebrae50a,50band50cwas illustrated without the locking screws20,21 in place on theplate2.FIG. 40 is a perspective view showing theplate2 ofFIGS. 1-5, at a stage of a surgical procedure when bone screws30 have been fully installed in threeadjacent vertebrae50a,50band50c, and lockingscrews20,21 have been rotated through an angle of about 90N to lock threebone screws30 in place; the left-hand locking screw20 as viewed has been rotated through an angle of about 60N to lock threebone screws30 in place and thecentral locking screw21 has been rotated through an angle of about 90N to lock two other bone screws30 in place. At this time, one of the camming surfaces44 of each lockingscrew20,21 rests atop thescrew head32 of arespective bone screw30.
• Installation of thelocking cap300 can also be performed with atool220 such as shown inFIGS. 41 and 42 having a suitablyshaped tip222 with a length corresponding to the depth ofhole306 in alocking cap300. Theend222 oftool220 is flared just proximal to the most distal end so that it creates a friction fit with thescrew cap300 for ease of manipulation, and prevents thescrew cap300 from falling off thetool200.
• FIG. 43 is a cross-sectional view in the plane of the center of the two end lockingscrew holes6 ofplate2, with twobone screws30 in their installed positions and lockingelement21 in its locking position.FIG. 44 is an enlarged view of one of the bone screws30 inplate2 ofFIG. 43. In a preferred embodiment, the axis of eachscrew30 is generally perpendicular to tangents to the upper and lower surfaces ofplate2 at points which are intersected by the longitudinal axis of the associatedbone screw30. Thus, because of the curvature ofplate2 in the plane ofFIG. 43, bone screws30 can be directed so as to converge toward one another at a desired angle. Preferably, such angle will be greater than 14°. More preferably, such angle will be greater than 14° and less than 30°. The axis of the twobone screws30 shown inFIG. 43 may subtend an angle of about 45N. Alternatively, the curvature of the plate from side to side may be so as to conform to the surface of the anterior aspect of the human adult cervical spine and the axis of the paired screw hole may deviate from being perpendicular to the plate when viewed on end to achieve optimal convergence.
• Because the bone screws30, once inserted, are locked to the plate, a “claw” of a rigid triangular frame structure is obtained at each pair of bone screws30 such that the attachment ofplate2 to thevertebral bodies50a,50band50cwould be highly secure due to the trapping of a wedged mass of bone material between the angled bone screws triangle, even if any thread stripping should occur. The “claw” may be further formed by three angled bone screws in a tripod configuration or by four bone screws in a four sided claw configuration.
• A plating system according to each of the above embodiments can be installed in the same manner as described above, and using the same instruments and tools, as illustrated and described above with respect to the first embodiment. In the case of the embodiment shown inFIG. 22, the compression operations would be performed by means ofslot232 instead of the middle lockingscrew hole12.
• 2. The Single Locking Plate Systems
• The single locking plate system will now be described.FIGS. 47-52 are views of a first embodiment of a single locking plate system. The contour ofplate600 is the same as theplate2 shown inFIGS. 1-5.Plate600 contains bonescrew receiving holes602 which are internally threaded603 for receiving corresponding locking elements in the form of alocking cap610, shown inFIGS. 56-59. For example, inplate600, thebone screw hole602 has an outer diameter of approximately 5 mm with a preferred range of 4-6 mm; and a threaded inner diameter of approximately 4.8 mm, with a range of 3.5-5.8 mm for this use. Attaching means other than threads may be used, such as bayonet type attachment elements.
• The bottom of each bonescrew receiving hole602 has an inwardly stepped portion of properly selected dimensions for retaining an associatedbone screw170, as shown inFIGS. 53-55. As described in greater detail below, in this embodiment, a single locking element in the form of alocking cap610 havingthreads608 shown inFIGS. 56-59, is associated with each of the bonescrews receiving holes602.
• The difference between thebone screw170 used in the single locking embodiment of the plate from the bone screw used in association with the multiple locking plate is essentially due to the fact that whereas in the multiple locking plate embodiment the locking elements slide over a portion of the top39 of thescrew head32, in the single locking embodiment thelocking cap610 fits over thehead172 of thebone screw170. Therefore, thehead172 of thebone screw170 of the present embodiment need not be smooth. This permits thehead172 of thisembodiment bone screw170 to be thicker and stronger.
• FIG. 65 shows twobone screws170 and associated threaded lockingcaps610 in their fully installed positions. In these positions,head portions174 and176 of eachbone screw170 form an interference fit with corresponding portions of an associated bonescrew receiving hole602.Rim612 of each threadedlocking cap610 forms an interference fit withupper portion178 of the head of its associatedbone screw170. Because thethread608 of each lockingcap610 mates precisely with the internal thread in an associated bonescrew receiving hole602, each threaded lockingcap610 is additionally subjected to a clamping force between associatedhead portion178 and theinternal threads603 of associated bonescrew receiving hole602. Therounded head614 of each threadedlocking cap610 assures that the upper surface of an assembled plating system will be free of sharp edges, or projections.
• Referring toFIGS. 80 and 81 tools for use in inserting both the bone screws and the locking cap in thesingle locking plate600 are shown. In the first embodiment of thedriving tool1000 shown inFIG. 80, thetool1000 has an outertubular housing1002. Within thehousing1002 is a torks type orhexagonal driver1004 that has a projectingend1006 that corresponds to therecess306 in thecap610 for engagement with thecap610. As indicated above, thedriver1004 is configured so that it makes a firm attachment for thelocking cap610 for holding thelocking cap610 firmly to the driver. Thehex driver1004 is hollow so as to be able to permit theshaft1010 of a Phillips or torks screw driver to fit through thehollow portion1012 for engagement by itstip1012 with thecorresponding recess180 ofbone screw170 for engagement by theend1006 of thedriver1004. Theshaft1010 of thedriver1000 is longer than the tubular housing anddriver1004 has an upper end (not shown) extending from the top end of thetubular housing1002 so that it can be rotated by the handle.
• Thehousing1002 has a diameter that permits thelocking cap610 to be held within the inner end of thetubular housing1002 by a friction fit or to thedriver1004. It is appreciated that other methods of holding thelocking cap610 within the end of thetubular housing1000 may also be employed.
• As shown inFIG. 80, the operation of the bone screw and lockingelement driver1000 is as follows: thecap610 is inserted onto the end of thecap driver1004, and then thecap driver1004 with theshaft1010 of the bone screw driver passing through the central longitudinal opening of the cap driver. As shown, the bonescrew driver shaft1010 passes through therecess306 in thecap610 and engages therecess180 in the head of thebone screw170. Thebone screw170 is shown being installed in a bone screw receiving hole in theplate600. The handle (not shown) of the bone screw driver is rotated, thereby screwing thebone screw170 in place. Since the diameter of the bone screw driver is less than the width of therecess306 of thecap610, the bonescrew driver shaft1010 is able to rotate without rotation of thecap610.
• The hollowtubular housing1002 rests on the top surface of theplate600 and assists in the alignment of theshaft1010 in relationship to the plate. Once thebone screw170 is inserted, thecap driver1004 is depressed until thethreads608 on the outside of thecap610 engages thethreads603 of the bone screw receiving hole. Thecap driver1004 is then turned until thecap610 is securely locked in place.
• InFIG. 81, an alternative embodiment of the combination bone screw and locking cap driver is shown. In this embodiment, a housing is not used. Instead, thedriver shaft1010 holds thecap610 by friction and thehandle620 for the bonescrew driver shaft1010 is rotated. Aball spring assembly622 holds thecap driver1002 up until the bone screw has been screwed into the bone screw receiving hole.Driver1010 has an elongated portion that once the bone screw has been installed, theball spring622 is depressed and thehandle624 associated with the cap driver is permitted to descend for rotation of thecap610. A tubular housing can be employed to assist in aligning of thecap610 in the bone screw receiving hole, as indicated above.
• The drivers shown inFIGS. 80 and 81 simplify the procedure, and reduce the number of instruments that are necessary to be used during the installation procedure. The procedure is quick and reliable, giving the physician more assurance that small watch parts will not be lost or difficult to manipulate.
• FIG. 52 is a top view of theplate600 partially installed, with threaded locking caps600 installed in bonescrew receiving holes602.
• FIGS. 53-55 show abone screw170 for use with the single locking plating system according to the invention.Bone screw170 differs frombone screw30 previously described in detail, only with regard to the stepped configuration ofhead172. Preferably,bone screw170 includes alower portion174 which is contiguous with the screw shank and has a reduced diameter equal to the maximum diameter of theshank176.Portion178 ofhead172 also has smaller diameter thanlower portion174. Thethread182 has the same configuration as for thebone screw30 discussed above. However, either embodiment of bone screws can be used with any of the plates.
• As in the case of the multiple locking plating system described above, the bone screws170 for use in the single locking plating system are preferably solid, where the screws adjoin the lower plate surface, where screws used with prior art plates are most prone to breakage, the only recess in the heads being for engagement of thetip222 of drivingtool220 and with the recess being above the critical area. Therefore, these bone screws170 remain robust. The screw heads are not deeply slitted into portions and the locking caps do not impose a radial outer force on the associated bone screw heads so the screw heads do not spread apart so as to be stressed and weakened.
• Referring toFIGS. 71, 73 and75 another alternative embodiment of the single locking plate system of the present invention is shown and referred to by thenumber500. Theplate500 has the same contour as theplate2 shown inFIGS. 1-5, but associated with each of thebone screw openings502, are threadedopenings524 offset from thebone screw openings502 for receiving thelocking element506,508, shown inFIGS. 72 and 74 as a threaded locking set screw or cap506 orscrew508.
• It is appreciated that other configurations of single locking plates may be employed. Referring toFIG. 82, asingle locking plate900 is shown in which there are a pair of bonescrew receiving holes910 at itsends930 and a number of bonescrew receiving holes950 along the longitudinal axis of theplate900. The additional bonescrew receiving holes950 permit a single plate to be able to be aligned with a number of different sized vertebrae disc spaces, and bone fusion grafts. As indicated above, the plate of the present invention shown inFIGS. 1-5, requires that a properly sized plate be selected by the surgeon so that each pair of bonescrew receiving holes6,8 line up with the appropriate vertebrae. This requires a number of different sized plates to be available for optimum attachment of the bone screw receiving holes to each of the vertebrae. With theplate900 ofFIG. 82, the close spacing and increased number of central openings permit the surgeon to locate at least one appropriate opening to be aligned with each of the intermediate vertebrae, and/or bone grafts.
• The procedure for installation of the single locking plates is substantially the same as described herein in detail for the multiple locking plates. The centrallongitudinal slot670 in the single locking plates is used for the compression procedure. The same instrumentation is used to create the plate hole either by means of a punch or a drill.FIGS. 60-69 show the various steps in the procedure for installation of the single locking plates, comparable to the steps employed in the installation of the multiple locking plates.
• Referring toFIGS. 76-79 theheads507 and526 of the lockingelements508 and522 have arecess510 and524 corresponding to the radius of thebone screw openings502 and528 so that the lockingelement508 and522 may be installed in place prior to the insertion of thebone screw170 into the bonescrew receiving hole502 and528. When the lockingelements508 and522 are rotated, a portion of its head extends over the top of the head ofbone screw170 to lock it in place. As with the above embodiments, the bottom surface of the locking screws508 and522 can have a camming or other configuration for engagement with thetop surface39 of the associatedbone screw170.
• While the plate instrumentation and method have been described in association with attaching a plate to the vertebrae of the spine, it should be appreciated that the plates can be adopted for specification to other parts of the body. See, for example, application Ser. No. 09/022,344, filed Feb. 11, 1998, and titled Skeletal Plating System, now U.S. Pat. No. 6,139,550, incorporated by reference above. However, the dimensions of the plate, the specific contours and placement of the bone screw receiving holes would have to be modified.
• Similarly, the bone screws described in this application could be used in other parts of the body, again being modified so as to serve their intended purposed, depending on the size of the body part in which they are to be installed.
• While particular embodiments of the present invention have been shown and described, it will be obvious to those skilled in the art that changes and modifications may be made without departing from this invention in its broader aspects and, therefore, the aim in the appended claims is to cover all such changes and modifications as fall within the true spirit and scope of this invention.
• While specific innovative features may have been presented in reference to specific examples, they are just examples, and it should be understood that various combinations of these innovative features beyond those specifically shown are taught such that they may now be easily alternatively combined and are hereby anticipated and claimed.

Claims (14)

1. A system for stabilizing a portion of the spinal column, comprising:

a plate including a length extending along a longitudinal axis and comprising at least a first end wall and a second end wall each extending transversely to said longitudinal axis; and

a holding instrument including a remotely actuatable holding system adapted to hold the plate with a clamping force between said first and second end walls.

2. The system ofclaim 1, wherein said first end wall forms an outer end surface of said plate and said second end wall is an end wall of a visualization opening extending through said plate.

3. The system ofclaim 1, wherein said holding system is adapted to hold said plate along said longitudinal axis of said plate.

4. The system ofclaim 1, wherein said holding instrument includes a proximal handle system and a connecting system operably connecting said holding system to said handle system.

5. The system ofclaim 1, wherein said first end wall is concavely curved and said second end wall is concavely curved, said holding system comprising a first holding member including a convexly curved plate contacting surface adapted to conform to the concavely curved first end wall and a second holding member including a convexly curved plate contacting surface adapted to conform to the concavely curved second end wall.

6. An instrument for holding an implant along a longitudinal axis of the implant, comprising:

an actuating system;

a connecting system extending proximally from said actuating system; and

a holding system at a distal end of said connecting system operably coupled to said actuating system with said connecting system, said holding system including first and second holding members moveable in the direction of the longitudinal axis of the implant with said actuating portion between a release position and a clamping position to selectively engage and release the implant.

7. The instrument ofclaim 6, further comprising a locking system at said actuating system to secure said holding mechanism in any one of a number of clamping positions.

8. The instrument ofclaim 6, wherein:

said first holding member comprises a first engagement member including a first contact surface; and

said second holding member comprises a second engagement member including a second contact surface.

9. A method for positioning a plate adjacent a spinal column of a patient, comprising:

accessing at least two vertebrae of the spinal column;

holding the plate along a longitudinal axis of the plate with a holding instrument; and

positioning the plate on the at least two vertebrae.

10. The method ofclaim 9, wherein holding the plate includes holding the plate between an end wall of the plate and an end wall of a visualization opening extending through the plate.

11. The method ofclaim 10, further comprising inserting a fusion device between the at least vertebrae before positioning the plate.

12. The method ofclaim 11, further comprising visualizing the inserted fusion device through the visualization opening.

13. The method ofclaim 9, further comprising securing the plate to the at least two vertebrae with bone engaging fasteners extending through the plate.

14. The method ofclaim 13, further comprising securing the bone engaging fasteners to the plate with at least one retaining device.

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